When a truck, trailer or some other vehicle is parked at a loading dock, often some sort of vehicle restraint is used to keep the truck from inadvertently moving away from an elevated platform of the dock. This allows a forklift truck to safely drive between the dock platform and the truck for the purpose of loading or unloading the cargo inside the truck.
There are a variety of vehicle restraints available that can be installed at a loading dock for engaging the truck's RIG (Rear Impact Guard), also known as an ICC bar. An ICC bar is a beam that extends horizontally across the rear of a truck, just below the truck bed. Its primary purpose is to prevent an automobile from under-riding the truck in a rear-end collision. However, not all trucks have an ICC bar that can be readily engaged by an ICC-style restraint, so in those cases a wheel restraint can be used for blocking one or more of the truck's wheels.
Perhaps the most common wheel restraint is simply a wheel chock that wedges between the driveway and the underside of the wheel. However, wheel chocks often slip out of position on driveways that are slippery due to oil, rain, ice, sand, gravel or dirt. Sometimes, wheel chocks wedge so tightly under the wheel that they become very difficult to remove. Trucks have also been known to drive completely up and over a wheel chock. Wheel chocks are often loose items that are not permanently attached to the loading dock area, so they tend to get misplaced.
One solution to the problems associated with manually installed wheel chocks can be found in U.S. Pat. Nos. 5,553,987 and 5,582,498. These patents disclose powered wheel restraints that travel along a track. However, such wheel restraints cannot always be readily installed at loading docks that may already have a drain or some other driveway irregularity situated where the track is to be installed.
A wheel restraint disclosed in U.S. Pat. No. 3,305,049 has a wheel chock that travels along a lead screw that is elevated above a driveway. However, there are some significant problems with the device. The chock always moves between its upright retracted position and its horizontally extended position at the same place along the lead screw, i.e., where the chock slides along the curved bar 26. If part of the truck/trailer happens to be at this location, that part could obstruct the movement of the chock. For example, such a part could include another wheel of the truck or trailer. And the location of the wheels is unpredictable due to the wide variety of trucks and trailers. Moreover, tools and other equipment are often stowed under the trailer, which could also obstruct the movement of the chock. The likelihood of hitting the stowed parts is increased, as the chock swings downward form a high, upright position. The higher up the chock reaches, the more likely it will reach the stowed parts. Damage may occur to the obstructing part or the wheel restraint itself if the lead screw continues to drive the chock regardless of any obstruction. Further, once the chock extends laterally outward, the lead screw drags the chock along the driveway until it reaches the first wheel. The dragging motion could plow quite an accumulation of snow and dirt up against the tire. Overtime, the dragging motion could eventually erode the surface of the driveway.
Another powered wheel chock system is disclosed in U.S. Pat. No. 5,709,518. The '518 device includes a sensor bar that swings a chock plate about a vertical axis at pivot hole. However, the device's ability to accommodate wheels of various diameters appears to be quite limited, as the distance between bar and chock plate is fixed. Increasing the distance between the bar and chock plate to match larger diameter wheels could create an interference problem between the chock plate and a forward set of wheels of a tandem axle trailer. The interference problem is worsened by the way the chock plate is first extended between the wheels and subsequently moved back against a front portion of the rear wheel. The additional backward movement requires additional space between a set of tandem wheels. The greatest space is at the lowest portion of the wheel; however, engaging a wheel at such a low point leads to other problems. If the chock plate, for instance, is too low, a truck may simply drive over it, especially if the truck/trailer is light (e.g., unloaded).
In addition to the specific problems of various powered wheel restraints, such wheel restraints in general are quite elaborate and expensive mechanisms. Thus, there is still a need for a simple yet effective way of restraining the wheel of a truck at a loading dock.